1. Field of the Invention
The present invention relates to a portable semiconductor storage device.
2. Description of the Related Art
FIG. 4 is a schematic cross-sectional view illustrating a conventional portable semiconductor storage device, for example, a memory card, which is disclosed in Japanese Published Patent Application 64-8877. FIG. 5 is a perspective view of the memory card. In FIGS. 4 and 5, a memory card main body 1 is sandwiched between conductive outer plates 2 and 3 which oppose each other. A printed board 4, on which semiconductor storage devices such as RAMs and ROMs (not shown) are mounted along with peripheral circuit devices (not shown), is housed in the memory card main body 1. Also, a terminal section 5 for making an electrical connection with external circuits is disposed in the memory card main body 1. The circuit ground (not shown) of the printed board 4 is connected to the conductive outer plates 2 and 3 via a ground member 6 and a ground spring 7. As a power source for the printed board 4, a cell 8 is housed in a cell holder 9 in the cell housing area 10 of the memory card main body 1.
The conventional portable semiconductor storage device is constructed as described above. The conductive outer plates 2 and 3 are connected to the circuit ground of the printed board 4 via the ground member 6 and the ground spring 7. The memory card main body 1 is constructed with the printed board 4, on which semiconductor storage devices are mounted, shielded from the ground. For this reason, this construction is effective in preventing data loss due to external noise, as well as the destruction of the storage device itself.
In the above-described portable semiconductor storage device, when a data backup function of a cell is required in a single device, the conductive outer plates 2 and 3 are connected to the circuit ground of the printed board 4. Therefore, the portable semiconductor storage device has a strong construction against data destruction due to external noise. However, when this device is mounted in a system, external noise is transmitted as ground superimposed noise. For this reason, an adverse influence on the stable operation of the entire system cannot be avoided. A problem arises, particularly in a case where the device is used in an application taking on an important function such as extended memory rather than data backup.
Also, the conventional construction of this device, the construction in which the conductive outer plates 2 and 3 are connected to the circuit ground of a board contained in the device, is complex. Thus, a problem arises, namely, mounting space and an assembly process for that connection are required.